Mixed concrete must be placed into a form. A form also often is called a formwork or shuttering. FIG. 17 shows concrete A placed into a formwork 30. The formwork 30 has a curved section 31. This section 31 is supported directly by a first support structure 33 that includes support materials 32 and curved support portions. The first support structure 33 is in turn supported by square steel bars 34 that are arranged perpendicular to the first support structure 33. Then, a support block 35 is used as an outermost support structure. The support block 35 is fixed to the formwork 30 by means of bolts 36 each having at one end a form tie 37 into which a wedge 38 is driven.
FIG. 18 also shows prior art. In FIG. 18, a curved metal pipe 39 is employed instead of the support block 35 of FIG. 17. As illustrated, the metal pipe 39 is fixed to the form 31 similarly to the support block 35.
Thus, FIGS. 17 and 18 depict two different techniques 35 and 39 for supporting a curved section of a formwork.
With the first technique of FIG. 17, however, it is costly and time-consuming to prepare many support blocks that each must have a curved surface similar to a particular curved portion of a formwork to be supported. Also, a support block with a particular degree of curvature cannot be used to support a curved portion of a formwork which has a different degree of curvature from the support block. Also, the support block is rather bulky and therefore takes up a lot of space when it is stored.
With the second technique of FIG. 18, it takes much time and trouble to curve plural metal pipes to particular degrees of curvature in the building site. Also, it is not easy to vary the curvature of a metal pipe already curved to some degree of curvature. In addition, a metal pipe is relatively bulky and therefore occupies no small space when it is stored.